Plug Unloader Using Low Force Actuator For Reciprocating Compressors

ABSTRACT

The advantages of plug type unloaders are well know and accepted by authorities such as American Petroleum Association as well as compressor and component manufacturers as well as users. There are further benefits to this device such as eliminating plug to valve misalignment and is lighter than other type unloaders. Field replacement of valve depressor unloaders is economically feasible and any type compressor valve that may be used.

RELATED APPLICATIONS

The present application is a continuation application of U.S. patent application, Ser. No. 61/139,084, filed Dec. 19, 2008, included by reference herein and for which benefit of the priority date is hereby claimed.

FIELD OF THE INVENTION

The present invention relates to reciprocating compressors and, more particularly, to unloading compressors.

BACKGROUND OF THE INVENTION

Nearly all reciprocating compressors are equipped with valve unloaders for load-less starting and/or capacity control. The usual unloaders are the valve plate depressor type which depress and hold the inlet valve plates open to prevent gas compression. Another type unloader called “plug type unloader” is commonly used. The plug type unloader opens and closes a hole in the center of the inlet valve to prevent gas compression.

Description of Prior Art

Problems with Value Plate Depressor Type Unloaders.

Ref FIG. 9.

(1) When used for start-up or capacity control are generally maintenance intensive when the associated inlet valve is designed for low mol weight gas such as hydrogen and start-up is with high mol weight gas such as air or nitrogen.

(2) Not practical for cylindrical valve elements such as poppets due to the multitude of depressors required per valve.

(3) Depressors are subject to operating problems due to high valve plate “drag forces” in reverse gas flow.

(4) Reverse flow forces can be significantly higher than normal flow by a factor of 3 or more and cause the inlet valve plates to warp thus reducing the effective plate lift and in some cases overpower the actuator.

(5) Proper clearance between unloader depressor and inlet valve must be maintained.

(6) Depressors must be matched to inlet valve for storage and use.

Other Solutions to Aforementioned Problems Include the Plug Type Unloader Previously Described.

Ref FIG. 8.

(1) Plug type unloaders are nearly maintenance free.

(2) Plug type unloaders are not affected by changes in gas mol weight.

(3) Plug type unloaders may be used with any type seal element.

(4) Plug type unloaders are not subjected to “drag forces”.

(5) Plug type unloaders function well in reverse or normal flow direction.

Shortcoming of Other Solutions.

(1) Plug type unloaders are subject to mis-alignment between the plug and flow hole.

(2) Plug type unloaders are more difficult to transport and install due to increased weight and size.

(3) Plug type unloaders are more expensive to manufacture.

SUMMARY OF THE INVENTION

Invention Description

In accordance with the present invention, there is provided a plug type unloader that can economically replace valve plate depressor type unloaders and be operated by a short stroke actuator. This self contained device uses the cylinder internal pressure as a stroke multiplier to move from loaded to unloaded positions depending on the position of the actuator plunger 46 (FIG. 6). The self contained device is mechanically attached to the inlet valve which eliminates any plug to valve mis-alignment and is much lighter than the conventional plug unloader assembly.

Advantages of Invention

(1) Eliminates problems associated with valve plate depressor type unloaders.

(2) Eliminates any plug to valve mis-alignment.

(3) Much lighter.

(4) Field replacement of valve depressor unloaders is economically feasible

(5) Multitude of inlet valves will generally be acceptable with fewer unloaders.

(6) There is no limit to type valve that may be used IE poppet, plate, ring.

(7) This plug type unloader is much less expensive to manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

A complete understanding of the present invention may be obtained by reference to the accompanying drawings, when considered in conjunction with the subsequent, detailed description, in which:

FIG. 1 is a section view of the device in closed position;

FIG. 2 is a section view of the device in open position;

FIG. 3 is a bottom section view of the device section 2-2 from FIG. 1;

FIG. 4 is an external view of the device showing flow cut-outs;

FIG. 5 is a section view of the device alternatives;

FIG. 6 is a composite view of the device with low force actuator in load position;

FIG. 7 is a side section view of a typical compressor cylinder;

FIG. 8 is a section view of a typical plug type unloader; and

FIG. 9 is a section view of a typical valve plate depressor unloader in unload position.

For purposes of clarity and brevity, like elements and components will bear the same designations and numbering throughout the Figures.

DESCRIPTION OF THE PREFERRED EMBODIMENT Component ID

-   main body 10. -   cover 11. -   piston and plug 12. -   flow cut-out(s) 14. -   variable gas pressure 16. -   check valve 18. -   vent valve 20. -   pressure chamber 22. -   vent pressure conduit 24. -   valve spring 26. -   check valve seat 28. -   opening spring 30. -   pressure seals 32. -   plug seat contained in main body 34. -   screw threads on main body 36. -   alternate cover 38. -   retaining studs 40. -   low force actuator 42. -   flow transfer element 44. -   actuator plunger 46. -   suction pressure 48. -   discharge pressure 50. -   compressor piston 52. -   front cylinder head 56. -   rear cylinder head 58. -   depressor attachment plate 60.

FIG. 7 is a section view of a reciprocating compressor cylinder offered for orientation purposes only. The compressor piston 52 moves to and fro between the front cylinder head 56 and the rear cylinder head 58. Suction pressure 48 is admitted through inlet valve 54 to variable gas pressure 16 region where it is compressed to discharge pressure 50 when the compressor piston 52 reverses direction and the volume between the compressor piston 52 and rear cylinder head 58 is reduced and the pressure is increased to discharge pressure 50. The present invention relates to replacing a valve depressor type unloader associated with inlet valve 54 by the present invention to improve operation and increase the overall compressor performance.

Heretofore it has been impractical to use a valve depressor (low force) type actuator for a plug unloader because the valve depressor type actuator plunger 46 (FIGS. 6, 9) usually does not have more than 0.375 inch (10 mm) “stroke” capability whereas a plug type can exceed 2 inches (50 mm) “stroke”. See FIG. 8 which is typical.

FIG. 1 is a section view of the device in the closed/loaded position, in accordance with the invention. In this position gas flows through the inlet valve 54 and the compressor operates normally as described above. The main body 10, cover 11, retaining studs 40 and inlet valve 54 form a container to include all the components. Check valve seat 28 and check valve 18 cooperate to admit pressure to pressure chamber 22 via flow transfer element 44 whenever pressure at variable gas pressure 16 is above the pressure on far side of check valve 18 which loads the piston and plug 12.

FIG. 2 is a section view of the device in the open/unloaded position. This position occurs when the vent valve 20 initiates venting by pressing on and closing check valve 18 which permits gas flow from the pressure chamber 22 via vent pressure conduit 24 which unloads the compressor cylinder end when the piston and plug 12 are retracted and gas flows in and out of the flow cut-out(s) 14 thus creating an unloading path 62. In this position gas does not flow through the inlet valve 54 in the normal manner because the variable gas pressure 16 region and suction pressure 48 are physically connected via flow cut-out(s) 14 and the compressor cylinder end is de-activated because any gas going into the compression space is expelled back to the suction pressure 48 when the compressor piston 52 reverses direction.

In summary, it can be seen that what is provided in this invention is a plug type compressor valve unloader that is functional as well as significantly smaller and lighter than conventional plug type unloaders. The device is mechanically attached to the inlet valve 54 thus eliminating any plug to valve misalignment experienced with the plug type unloader shown in FIG. 8. There is no limit to type valve that may be used, IE poppet, plate, ring. Field replacement of valve depressor unloaders is economically feasible since most existing valve plate depressor actuator(s) may be reused.

Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the invention is not considered limited to the example chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention.

Having thus described the invention, what is desired to be protected by Letters Patent is presented in the subsequently appended claims. 

1. A plug unloader using low force actuator for reciprocating compressors for de-activation of compressor cylinder ends, comprising: means for allowing gas flow when open; means for opening and closing said allowing gas flow when open; means for creating force for said allowing gas flow when open; means for converting variable pressure to constant pressure; means for venting pressure in said creating force for said allowing gas flow when open; means for blocking flow when pressure is less than said creating force for said allowing gas flow when open; and means for allowing gas flow through said allowing gas flow when open.
 2. The plug unloader using low force actuator for reciprocating compressors in accordance with claim 1, wherein said means for allowing gas flow when open comprises an unloading path.
 3. The plug unloader using low force actuator for reciprocating compressors in accordance with claim 1, wherein said means for opening and closing said allowing gas flow when open comprises a piston and plug.
 4. The plug unloader using low force actuator for reciprocating compressors in accordance with claim 1, wherein said means for creating force for said allowing gas flow when open comprises a pressure chamber.
 5. The plug unloader using low force actuator for reciprocating compressors in accordance with claim 1, wherein said means for converting variable pressure to constant pressure comprises a check valve.
 6. The plug unloader using low force actuator for reciprocating compressors in accordance with claim 1, wherein said means for venting pressure in said creating force for said allowing gas flow when open comprises a vent valve.
 7. The plug unloader using low force actuator for reciprocating compressors in accordance with claim 1, wherein said means for blocking flow when pressure is less than said creating force for said allowing gas flow when open comprises a check valve seat.
 8. The plug unloader using low force actuator for reciprocating compressors in accordance with claim 1, wherein said means for allowing gas flow through said allowing gas flow when open comprises a flow cut-out(s).
 9. A plug unloader using low force actuator for reciprocating compressors for de-activation of compressor cylinder ends, comprising: an unloading path, for allowing gas flow when open; a piston and plug, for opening and closing said allowing gas flow when open; a pressure chamber, for creating force for said allowing gas flow when open; a check valve, for converting variable pressure to constant pressure; a vent valve, for venting pressure in said creating force for said allowing gas flow when open; a check valve seat, for blocking flow when pressure is less than said creating force for said allowing gas flow when open; and a flow cut-out(s), for allowing gas flow through said allowing gas flow when open.
 10. The plug unloader using low force actuator for reciprocating compressors as recited in claim 9, further comprising: a main body, for housing parts.
 11. The plug unloader using low force actuator for reciprocating compressors as recited in claim 9, further comprising: a vent pressure conduit, for connection to pressure chamber vent region.
 12. The plug unloader using low force actuator for reciprocating compressors as recited in claim 9, further comprising: a valve spring, for closing said vent valve and said check valve.
 13. The plug unloader using low force actuator for reciprocating compressors as recited in claim 10, further comprising: a vent pressure conduit, for connection to pressure chamber vent region.
 14. The plug unloader using low force actuator for reciprocating compressors as recited in claim 10, further comprising: a valve spring, for closing said vent valve and said check valve.
 15. The plug unloader using low force actuator for reciprocating compressors as recited in claim 11, further comprising: a valve spring, for closing said vent valve and said check valve.
 16. The plug unloader using low force actuator for reciprocating compressors as recited in claim 13, further comprising: a valve spring, for closing said vent valve and said check valve.
 17. A plug unloader using low force actuator for reciprocating compressors for de-activation of compressor cylinder ends, comprising: a main body, for housing parts; an unloading path, for allowing gas flow when open; a piston and plug, for opening and closing said allowing gas flow when open; a pressure chamber, for creating force for said allowing gas flow when open; a check valve, for converting variable pressure to constant pressure; a vent pressure conduit, for connection to pressure chamber vent region; a vent valve, for venting pressure in said creating force for said allowing gas flow when open; a valve spring, for closing said vent valve and said check valve; a check valve seat, for blocking flow when pressure is less than said creating force for said allowing gas flow when open; and a flow cut-out(s), for allowing gas flow through said allowing gas flow when open. 